The present invention relates to a roll, especially a roll used under hot condition such as rolls for hot rolling or continuous casting.
Rolls for hot rolling or for continuous casting are used under conditions where metal pieces heated to 600.degree. C..1100.degree. C. directly contact a roll surface repeatedly or, according to circumstances, the metal pieces temporarily stop at a roll. Accordingly, the surface layer of such a roll is radically heated and cooled and a large quantity of thermal stress occurs on the surface layer which results in plastic deformation of the surface layer. Also bending stresses occur by mechanical loads applied on the surface layer part of a roll. Cracks occur on such surface layer because of the thermal stress and the bending stress. Furthermore, such cracks grow into the inside of the roll, and in some cases the cracks cause breakdown of the roll.
The above mentioned conditions apply to a roll operating under hot conditions. When a roll operating under cold conditions, cracks are caused on the surface layer by a repetitive mechanical load, and further, the cracks grow into the inside of the roll so that it is considered that a roll operating under such cold conditions is the same as a roll operating under hot conditions. In an attempt to provide for such conditions, it has been considered to provide a built-up weld on the surface layer of a roll by using crack-resistant materials. However, even if such excellent materials were used on a roll, it is impossible to completely prevent crack initiation on the roll and their growth with the passing of time. Also, the method where a built-up weld is generally sets the weld beads in a spiral manner has the problem that cracks are caused along the weld beads and such cracks easily connect in a circumferential direction of the roll body.